iPhone XR screen goes black during phone call

It could be a glitch of your proximity sensor.

Check that your screen protector doesn't obstruct that sensor, close to your XR earpiece (in the notch). If you have doubts, try removing your screen protector.

The correct behavior is: when you hold the iPhone close to your ear, the screen turns black. When you remove your iPhone from your ear, the screen (speaker and other functions included) should reappear on your screen.

If the issue still persists, try a forced restart of your device:--> Force restart iPhone – Apple Support

If you get no help, contact Apple Support:--> Get Support

Regards

Giulio

The notch on top area of screen. Where the front camera, and ear piece located.